1. Field of the Invention
In general, the present invention relates to filter devices that are contained within the confines of a storm drain. More particularly, the present invention relates to the structure of such filters and the support devices used to position such filters within the storm drain.
2. Description of the Prior Art
In civil engineering design, many modern streets are designed and built with storm drains. The storm drains are periodically located along the curb of the street. The street is graded in such a manner so that any water falling onto the street will flow to one of the storm drains. This prevents water from collecting on the street and inhibiting the flow of traffic along the street.
Traditionally, curbside storm drains contain a catch basin that is connect to a below lying sewer with a large diameter pipe. The catch basin is commonly covered with a grate. The grate enables water to flow into the catch basin but prevents large objects, such as tree branches, from passing into the catch basin and blocking the sewer pipe. The catch basin itself collects debris that is heavier than water but is washed into the storm sewer by the force of flowing water. As a result, storm drains need periodic maintenance, wherein the debris collected in the catch basin is removed.
As water flows over a street to a storm sewer, the water often mixes with oil and other contaminants. The oil comes from automobiles that leak oil. Other petroleum based contaminants include grease, diesel fuel, hydraulic fluid and gasoline. The federal and state environmental protection laws set forth many guidelines governing the disposal of petroleum based contaminants. Generally, it is unlawful to dispose of petroleum based contaminants in the public sewer system or in any other flowing supply of water. As such, the rain runoff that passes into many curb side storm drains fails to meet the state and federal standards due to the petroleum based contaminants that wash into the storm drains with the rain water.
The prior art contains many different types of filter systems that are intended to at least partially purify the runoff water that passes into a storm drain. Certain prior art devices are filters that pass over the grate above the storm sewer. Such a filter is exemplified by U.S. Pat. No. 5,403,474 to Emery, entitled Curb Inlet Gravel Sediment Filter. In such prior art arrangements, the filter itself is accessible above the sewer's grate. Consequently, the filter disrupts the smoothness of a street's surface and therefore is only good in certain temporary applications.
Since the catch basins of many storm drains are made of poured cement, it is not practical to change the structure of existing storm drains in order for those storm drains to accept filters. As a result, many filter configurations have been made that are adapted to be added to existing storm sewer designs. In a typical storm sewer, a ledge is formed around the to rim of the catch basin. The drain grate rests upon the ledge, thereby covering the open top of the catch basin. The depth of the ledge typically corresponds to the thickness of the grate. As a result, the top of the grate will lay in the same plane as does the surface of the street.
In the prior art, there are filter structures that hang in the storm drain catch basin below the grate. Typically, such prior art filter structures engage the same ridge of the catch basin that supports the grate. As a result, a portion of the filter structure must be place in between the grate and the ridge upon which the grate was designed to sit. Such prior art filter structures are exemplified by U.S. Pat. No. 5,223,154 to MacPherson, entitled System For Filtering Liquids In A Catch Basin Using Filters In Series And Overflow Channels; U.S. Pat. No. 5,372,714 to Logue, entitled Storm Sewer Catch Basin And Filter and U.S. Pat. No. 5,284,580 to Shyh, entitled Refuse Collecting Frame For Sewer. One of the problems associated with such prior art filter structures is that the presence of the filter structure under the grate prevents the grate from seating properly onto the ridge at the top of the catch basin. As a result, the grate is held above its normal height, which may cause the grate to protrude above street level. If the grate does extend above street level, the grate becomes a tripping hazard. Furthermore, the grate can be caught by street plows and car tires, wherein the grate can be damaged or accidentally moved out of place.
U.S. Pat. No. 5,925,241, entitled Storm Drain Filter, and U.S. Pat. No. 6,368,499, entitled Storm Drain Assembly With Disposable Filter Cartridge, both belong to the applicant herein. In these patents, the applicant invented a filter structure that can be retroactively attached to a storm drain in a manner where the filter element does not extend above street level or cause the grate of the storm drain to extend above street level. However, in both patents, the filter is the same size as the sewer grate. Consequently, all the water that falls through the sewer grate flows through the filter. Although, this provides good filtration to the water, in certain situations the configuration can cause problems.
During normal rain conditions, water flows into the grate of a sewer at a controlled rate. The water therefore falls through the sewer grate before the water travels more than six inches across the top of the sewer grate. As a consequence, the vast majority of water that flows into a sewer grate passes only through the peripheral areas of any filter that is supported below the sewer grate. The area in the center of the sewer grate receives a relatively small amount of water.
However, during a heavy rain, the flow of water into a sewer grate can exceed the capacity of the sewer grate to receive water. Water therefore pools above the sewer grate and flows into the sewer grate at all points. It is also during period of heavy rain that a great deal of debris can be washed into a sewer grate. Certain types of debris, such as pine needles, leaves, paper, plastic bags and the like can pass through the sewer grate and become stuck on the filter suspended below the sewer grate. Once this happens, the filter becomes obstructed and the flow capacity of the sewer grate is greatly reduced.
A need therefore exits for a filter system for a sewer grate that can filter water during normal rain conditions, yet does not clog or otherwise restrict sewer flow capacity during heavy rain conditions. This need is met by the present invention as described and claimed below.